The following will be determined: 1. The genetic control of repair replication, and 2. of liquid holding recovery; 3. the role of DNA polymerase I in postreplication repair; 4. the effect of a uvrD mutation on excision repair; 5. the phr gene has been found not to be located where reported in the literature, its correct location is being determined; 6. a new repair deficient strain of E. coli has been found to be nonmutable by UV radiation and will be further characterized; 7. human fibroblasts sensitive to X radiation are being sought from patients who have shown an unusually severe skin reaction during radiation therapy.